FreeBSD slices and the Boot Manager

Teske, Devin Devin.Teske at
Sun Jul 28 22:23:43 UTC 2013

On Jul 28, 2013, at 12:55 PM, Conny Andersson wrote:

> Hi Ian,
> Thank you for all of your advices regarding my questions. I have been using FreeBSD for more than ten years, but I never heard of sade (sysadmins disk editor). That is one of the joyful things with running FreeBSD/Unix; there is always something earlier unheard of to explore. And, there is always more than one way to approach a problem.

In this case, sade is (or was) a direct by-product of the death of sysinstall(8). It only exists in 9 or higher.

In-fact... sade was (up until recently in HEAD) actual code removed from sysinstall(8).

NOTE: In HEAD, sade(8) is now a direct path to "bsdinstall partedit"

I don't know what the long-term goals are for sade, but it's a nice 4-letter acronym that's a nice keystroke saver (at the very least).

>> On Mon, 29 Jul 2013, Ian Smith wrote:
>> In freebsd-questions Digest, Vol 477, Issue 8, Message: 10
>> On Sat, 27 Jul 2013 19:39:30 +0200 (CEST) Conny Andersson <ataraxi at> wrote:
>> > Hi,
>> >
>> > I have a workstation with two factory installed hard disks. The first disk,
>> > ada0, is occupied by a Windows 7 Pro OS (mainly kept for the three year
>> > warranty of the workstation as Dell techs mostly speak the Microsoft
>> > language).
>> Yes, best humour adherents of the Almighty Bill - keeps them sweet.
>> > Instead I have configured the BIOS to boot from the MBR on the second disk
>> > as I most of the time (99%) use FreeBSD. The MBR on ada1 was installed with
>> > sysinstall's option "Install the FreeBSD Boot Manager", when I installed
>> > the FreeBSD 8.3-RELEASE.
>> Right.  sysinstall(8) - or at least the fdisk and bsdlabel modules that
>> constitute sade(8) - remains the only safe and sane way to handle MBR
>> disks.  bsdinstall seems fine for GPT, but its paradigm doesn't play so
>> well with trying to do the sorts of manipulations you're talking about
>> here.  Why noone's tried to update sade(8) for GPT I don't understand;
>> it's a far better, more forgiving interface, in my old-fashioned? view.
>> > (The latest BIOS version 2.4.0 for Dell T1500 does not support
>> >
>> > The second disk ada1, now has three FreeBSD slices:
>> >
>> > 1) ada1s1 with FreeBSD 8.1-RELEASE
>> >
>> > 2) ada1s2 with FreeBSD 8.2-RELEASE
>> >
>> > 3) ada1s3 with FreeBSD 8.3-RELEASE
>> >
>> > I want to install the new FreeBSD 8.4-RELEASE on ada1s1 by overwriting the
>> > now existing two first slices. This means that ada1s3, must become ada1s2
>> > instead. Is this possible to do?
>> Yes and no.  Using sysinstall|sade on my 9.1 laptop -- without setting
>> sysctl kern.geom.debugflags=16 so it can't write any inadvertent changes
>> to my disk :) -- in the fdisk screen you can delete the first two slices
>> freeing their space for a new slice (or two) and you can then allocate
>> s1 ok, but the existing s3 is still called s3.  Would that be a problem?
>> If you only created one slice there you'd have s1 and s3, with s2 and s4
>> marked as empty in the MBR shown by fdisk(8).  MBR slice order need not
>> follow disk allocations, eg s4 might point to an earlier disk region.
>> sysinstall|sade has undo options for both fdisk and bsdlabel modules;
>> it's easy to play with, no chance of damage - even with foot-shooting
>> flag set, unless/until you commit to changes.  If in doubt hit escape
>> until it backs right out, nothing will be written.
>> > A very important question is if sysinstall's option "Install the FreeBSD
>> > Boot Manager" detects that I have a FreeBSD 8.3 and detect it as slice 2 on
>> > disk 1? So it becomes a boot option when I am rebooting? (Maybe the slice
>> > may come up as ad6s2, because AHCI in FreeBSD 8.4 isn't enabled at the time
>> > of the install.)
>> If you're running 8.4 sysinstall as init, ie booted into the installer,
>> and you've told it to install to s1, then it should set s1 as the active
>> partition in the disk table and in boot0cfg's active slice table.  I've
>> never tried it with a second disk so I can't confirm that will all play
>> nice, but you seem to have installed 3 versions ok before :)
>> If not, you can run boot0cfg(8) anytime to set the active slice etc, so
>> that shouldn't be a worry.  Likely need to set debugflags=16 to do that
>> on a running system also .. don't forget to set them back to 0 later!
>> (For anyone) still nervous about sade for setting up MBR disks, play
>> with a spare memstick, setup a couple of slices, boot0cfg etc, allocate
>> and delete slices and partitions.  Jordan got that together >15years ago
>> so noone would ever need to do those icky slice/partition maths again.
>> My theory: few have been brave enough to dare mess with $deity's work,
>> though it just needs some updates for modern realities, not abandonment.
>> [ Polytropon, it's not 'obsolete' at all; still in 9 anyway.  It'll be
>> obsolete when there are no more MBR-only systems in use - say 7 years -
>> OR when bsdinstall incorporates all the missing good sade(8) features,
>> which requires it making a clear distinction between GPT and MBR and
>> working accordingly, including cleaning up GPT stuff if MBR chosen.  At
>> 9.1-R anyway, it doesn't do it so well for MBR.  Try installing over an
>> existing desired slice partitioning, newfs'ing everything EXCEPT your
>> valuable /home partition.  Not for beginners, yet simple in sade(8) ]
>> > If the answer to these questions is yes, then the next two questions arise.
>> >
>> > Can I mount ada1s2a (FreeBSD 8.3) from the newly installed FreeBSD 8.4 and
>> > edit my FreeBSD's 8.3-R /etc/fstab according to the new disk layout, and
>> > occasionally run FreeBSD 8.3 without problems? Or do I have to do more to
>> > get it to work?
>> Except it likely will still be called ada1s3a, it should be no problem.
>> Once boot0cfg(8) is working right, you can boot from any bootable slice;
>> it 'knows' but doesn't care what (if any) OS is on any other slices.
>> > The idea behind this kind of 'reverse' disk layout of mine is to have
>> > FreeBSD 8.4 as my new default OS. And have FreeBSD 8.3 untouched for
>> > configuring FreeBSD 8.4 and booting into it when ever needed. If I can do
>> > this as described above, I will have plenty of space on the disk for the
>> > future and a new FreeBSD release.
>> Sure.  Another option would be a much smaller new s2 after the bigger s1
>> as a 'transit lounge' between slices, I use such for config backups etc.
>> Speaking of which, given that you're all safely backed up, nothing can
>> go wrong, right? :)
>> cheers, Ian
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